This disclosure relates to a thermocline storage tank suitable for use in a solar power system, for example.
Typically two large storage tanks are used for molten salt thermal storage solar plants (power tower or trough designs). These tanks typically can hold well over 50 million pounds of salt each and measure over 125 ft (38 m) in diameter and over 40 ft (12 m) tall. In a power tower system the cold tank is typically fabricated out of a carbon steel material and stores salt at about 550° F. (288° C.). The hot tank can typically be fabricated out of a stainless steel or other high strength alloy and stores salt at about 1050° F. (566° C.).
Each tank is sized to store the entire plant working inventory of molten salt. In the morning, cold salt at 550° F. (288° C.) is pumped out of the cold tank into the solar energy receiver where it is heated to 1050° F. (566° C.) and then stored in the hot tank. When required to produce steam and electrical power, hot salt is pumped out of the hot tank and sent to the steam generator system where it is cooled back to 550° F. (288° C.) and returned to the cold thermal storage tank. In this fashion, salt is “shuttled” back and forth between the two tanks following a diurnal cycle. Thus, there is twice the storage capacity in the combined volume of the two tanks as there is molten salt. At times one tank is generally full and the other generally empty and other times both tanks are partially full.
Salt tanks for large solar power plants are quite expensive and include electrical heat tracing or other forms of heaters, thermal insulation, cooled foundation, instrumentation, and other supplementary equipment including a support structure. To date, designers have studied replacing the hot and cold tanks with a single tank but have not solved the problem of effectively and efficiently precluded the mixing of the hot and cold fluids in a single tank.